The satellites were stowed aboard an Atlas V rocket flying in the 401 configuration — a four-meter fairing, no solid-rocket boosters, and one engine in the Centaur upper stage.

Each of the two spacecraft carries the same complement of instruments, which includes five built by Aerospace.

Called the Radiation Belt Storm Probes (RBSP) mission, it is part of NASA’s Living With a Star Geospace program to explore fundamental processes that operate throughout the solar system, in particular those that generate hazardous space weather effects near Earth and phenomena that could affect solar system exploration.

The instruments on the two RBSP spacecraft will provide the measurements needed to characterize and quantify the processes that produce relativistic ions and electrons. They will measure the properties of charged particles that comprise the Earth’s radiation belts and the plasma waves that interact with them, the large-scale electric fields that transport them, and the magnetic field that guides them.

Understanding the radiation belt environment and its variability has extremely important practical applications in the areas of spacecraft operations, spacecraft and spacecraft system design, mission planning, and astronaut safety.